Plastic dehydrogenation facilitates the revalorization of discarded plastic. Compared with conventional plastic pyrolysis, microwave catalysis can achieve higher H₂ yield and conversion in a shorter time. The effects of different structures of iron-based catalysts on the H₂ yield in microwave field were studied, and the interaction mechanism between catalyst composition and dehydrogenation activity of plastic was discussed. Results showed that Al₂O₃-loaded iron catalysts and Fe-Al composite oxides can obtain high H₂ yield and promote the generation of carbon nanotubes, with the latter achieving H₂ yield up to 46 mmol/g. The microwave absorption properties, iron morphology, and dispersion of the catalysts play important roles in the dehydrogenation of plastic under microwave fields, as shown by X-ray diffractometry and Mössbauer spectroscopy. Furthermore, the effect of a microwave field shielded by a SiC tube reactor on the dehydrogenation of plastic was investigated. The results show that the amount of dehydrogenation of plastic in the SiC tube reactor decreases significantly under the same temperature conditions, which proves that the microwave field has a favorable effect on the dehydrogenation of plastic.